You should be able to get the Mac to recognize the MBox as a straight USB device without ASIO. ASIO is special software that makes it much easier to manage overdubbing and multitrack without delays. Adding ASIO to Audacity is possible, but needs a very advanced user, and sometimes even then.
Plug in the MBox and open Apple > System Preferences > Hardware > Sound > Input. Do you see the device listed there? Does the blue-ball sound meter jump when you talk or sing? If the Mac system can’t see the MBox, then Audacity will never work right.